ELECTRICAL PRODUCTS--ALUMINUM.
Another comparatively new article of manufacture now produced in large
quantities at Niagara Falls is aluminum. Until within the last few years
this metal was not used to any extent by manufacturers, because of the
great expense attending its production. Now, however, it is produced in
such quantities as to make it about as cheap as brass, bulk for bulk.
Aluminum is a very light metal, with a color somewhat lighter than
silver; its specific gravity being about one-third that of iron.
Aluminum is found in one of its compounds in great quantities in nature,
especially in certain kinds of clay and in a state of silicate, as in
feldspar and its associated minerals. It is found in great quantities in
southern Georgia, where it is mixed with the red oxide of iron that
abounds in that region. Here, it exists as alumina, which is an oxide of
aluminum. Before it is taken to the reduction-works the alumina is
separated from all other substances. It is a white powder, tasteless,
and not easily acted upon by acids.
Electricity is the chief agent in the production of metallic aluminum.
The reduction company buys this alumina, which has been separated from
the clay or ores where it is mined. In a large room there are located a
great number of iron vats or crucibles, lined with carbon, about two or
two and one-half feet deep, five or six feet long and four feet wide.
Immediately over each vat is constructed a metal framework, through
which are inserted a large number of carbon rods about eighteen or
twenty inches long and from two to two and one-half inches in diameter.
This framework is electrically insulated from the iron crucibles. The
framework and the carbons are connected with the positive conductor of
the electric current, and the vat or crucible with the negative. These
conductors are very large, something like a foot in width and an inch in
thickness, and made of some good conductor of electricity. They have to
be very large because they carry a current equal to 3050 horse-power.
The current is one of great volume, but very low voltage; the
electromotive force at each vat or crucible being only about seven
volts. As the process is electrolytic, and not simply a heating process,
the direct current must be used, and therefore the current coming from
the power-house must be transformed twice; first to bring it to a
proper voltage and secondly to change it from an alternating to a direct
current. These iron vats or crucibles are connected up in series,
electrically, and then they are filled with the alumina and certain
other materials, which act either as a flux or as a means of increasing
the conductivity of the mixture; just what this substance is, is
probably one of the secrets of the process. When all of the crucibles
are filled with the mixture the current is turned on and is kept on
continuously night and day seven days in the week. All of the material
in the different crucibles is heated to redness, when the process of
separation takes place. The oxygen of the alumina is thrown off as a
gas, and other residuum floats to the top of the crucible and is skimmed
off.
Metallic aluminum in a melted state sinks to the bottom of the crucible,
where it is dipped out from time to time with large iron ladles and
poured into sand and molded into blocks similar to that of pig iron.
From time to time, as the metal is dipped out, fresh alumina with the
other substances are thrown in on top of the crucible, so that the
process is continually going on, day and night, week in and week out.
The heat in the process of reducing alumina, as we have before seen, is
not the chief factor; it simply serves to reduce the compound to a fluid
state so that the electrolytic action can readily take place.
Therefore it is not necessary to be brought to a white heat, as it is in
the case of the production of carborundum, described elsewhere.
It was extremely interesting to observe the wonderful magnetic effects
that were produced in iron when brought into proximity with these
enormous electrical conductors. The voltage was so low that one could
handle them with impunity. The iron crucibles became so magnetic that a
heavy bar of iron seven or eight feet long would cling to their sides,
so that it would be held in an upright position. Bars of iron would
cling to the conductor at any point along its length, and, although
these conductors were carrying an energy of over 3000 horse-power, they
produced no perceptible effect upon the human body. The reason for this
lies in the fact, first, that the body is not made of magnetic material,
and, secondly, the pressure is so low that the body--being a poor
conductor--would not easily allow the low-pressure current to pass
through it.
Aluminum is fast becoming an important article of commerce, and it is
destined to become more and more so on account of its extreme lightness
as compared to other metals.
It is found to be valuable also when used as an alloy with many of the
other metals. One of the great drawbacks to its more extensive use lies
in the fact that as yet no satisfactory method has been devised for
soldering it. Undoubtedly in time this difficulty will be solved, when
its use will be greatly increased. It is estimated that in its various
compounds aluminum forms about one-twelfth of the crust of the earth.